In the case of conventional automatic ice makers and ice-maker trays, such as, for example, known from U.S. Pat. No. 6,571,567 B2, the individual compartments in which the ice is produced are substantially block-shaped. This shape does indeed enable a good utilisation of space, but has the disadvantage that removal of the finished pieces of ice from the mould is difficult, since when a piece of ice begins to detach from the base of its compartment there arises between it and the base a cavity in which underpressure prevails. This keeps the piece of ice in its position as long as a pressure equalisation between this cavity and the environment is not produced.
In the case of an independent ice-maker tray not fixedly incorporated in an appliance a user can gain assistance in that when the pieces of ice are ready the user knocks out, with the open side of the compartments downwards, on a firm support. Such a brisk blow can readily detach the pieces of ice sufficiently far from the compartment base to enable flowing on of air. However, this solution is not satisfactory, since the pieces of ice usually also hit the support violently and in that case are scattered or even damaged.
This method for removing the pieces of ice from the mould is not usable for an automatic ice maker. A widespread approach for solving the problem of removal from the mould is here to mount at the ice-maker tray an electric heating device which is placed in operation when the pieces of ice are ready in the compartments, in order to thaw these at the surface. However, a satisfactory solution of the problem is also not thereby achieved, because the water film arising in the case of thawing has a tendency, due to capillary forces, to wet the entire surface at which the piece of ice and compartment are in contact. If the ice-maker tray with pieces of ice thawed at the surface is turned upside down then the own weight of the pieces of ice does indeed have the effect that these slightly move away from the compartment base, but the thereby created intermediate space is filled by water which has to be sucked away from the gaps between the ice block and the side walls of the compartment while overcoming the capillary forces arising there. As long as this water draws back from the gap between the piece of ice and the at least one side wall of the compartment towards the base it very consistently prevents penetration of air between the piece of ice and the base of the compartment. Removal from the mould can thereby initially be even more difficult than in the case of pieces of ice which are not thawed, as can be readily established experimentally if an ice-maker tray with only slightly thawed pieces of ice is hit on a support. Only when with an increase in thickness of the water layer a sufficiently wide intermediate space between the piece of ice and the walls of the compartment is created can air actually penetrate between the piece of the ice and the compartment base and the piece of ice drops out of the compartment.
Obviously this solution is also not completely satisfactory, because the necessity of partly thawing again already finished pieces of ice causes a not inappreciable energy consumption of the ice maker and it loads the energy balance of a refrigerating appliance in which such an ice maker is used.